Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to adaptive frequency-hopping oscillators and phase-locked oscillators. More particularly, the present invention pertains to phase-locked oscillators with adaptive circuitry, to lead-compensated digital integrators for use in phase-locked oscillator, and to nonlinear D/A converters for use in learning systems such as adaptive frequency-hopping oscillators.
2. Description of the Related Art
Frequency-hopping transmitters are capable of transmitting radio frequencies on successive ones of a plurality of individual output frequencies with the output frequencies chosen in accordance with a code for a particular day or period.
Since the transmitted information remains on a given frequency for a matter of seconds, or microseconds, and since the order of selection of frequencies can be changed rapidly and precisely, information can be successfully encoded by the use of frequency-hopping transmitters.
As an example, when used to transmit video signals, a frequency-hopping transmitter could transmit each successive scan line at a different frequency.
The individual output frequencies are called channels, and the process of dividing a range of frequencies into channels is called channelizing. Each channelized frequency is produced by applying a selective voltage to a voltage controlled oscillator, and the selective voltages that will drive the voltage controlled oscillator to the channelized frequencies are called channelizing voltages.
Frequency-hopping oscillators can be designed to learn channelizing voltages for a particular voltage controlled oscillator, to correct for errors of proportionality and nonlinearity of analog components, and to correct for temperature-caused drift of analog components. Learning systems are sometimes called adaptive systems or adaptive learning systems.
Charavit et al., in U.S. Pat. No. 4,511,858, issued Apr. 16, 1985, teaches embodiments of phase-locked oscillators that use analog integrators. Their phase-locked oscillators are adaptive in that channelizing voltages are stored, recalled, corrected through a phase-locked loop, and placed again in storage.
A frequency-hopping transmitter is a transmitter that utilizes a frequency-hopping oscillator. In like manner, a frequency-hopping receiver is a receiver that utilizes a frequency-hopping oscillator. A frequency-hopping oscillator is a phase-locked oscillator that is channelized and whose channelized frequencies can be accessed rapidly in response to a predetermined program.
Phase-locked oscillators are used in transmitters for producing an output frequency that is crystal referenced, for demodulating frequency modulated signals in radio receivers, to achieve frequency deviation compression in frequency-modulated and phase-modulated receivers, and in various devices in which both rapid change to selected frequencies and precise frequency control are critical.
The use of phase-locked oscillators to achieve frequency deviation compression in radio receivers is taught by Lautzenhiser in U.S. Pat. No. 5,091,706, issued Feb. 25, 1992; in U.S. Pat. No. 5,497,509, issued Mar. 5, 1996; and in U.S. Pat. No. 5,802,462, issued Sep. 1, 1998.
Phase-locked oscillators can be AC modulated, DC modulated, or both, as taught by Lautzenhiser in U.S. Pat. No. 5,091,706; in U.S. Pat. No. 5,097,230, issued Mar. 17, 1992; and in U.S. Pat. No. 5,311,152, issued May 10, 1994. In addition, phase-locked oscillators can be channelized as also taught by the aforesaid Lautzenhiser patents. Frequency-hopping oscillators may be AC and/or DC modulated using principles taught in the aforesaid Lautzenhiser patents.
A phase-locked oscillator includes both a forward path and a feedback path. As defined herein, the forward path extends from a comparing device, or phase detector, through a VCO, to an output frequency conductor. The feedback path extends from the output frequency conductor, through one or more frequency dividers which serve as channelizing devices and/or other devices in the feedback path, to the comparing device. In accordance with these definitions, the comparing device is not a part of either path.
In phase-locking oscillators, both the forward path and the feedback path are connected to a crystal-controlled reference oscillator by a comparing device. Phase lock is achieved when a feedback frequency from a voltage controlled oscillator equals the frequency of the reference oscillator.
Channelization of phase-locking oscillators is achieved by channelizing the feedback path. The feedback path is channelized by dividing frequencies in the feedback path by N, as shown herein, by any of the ways taught by Lautzenhiser in the aforesaid patents, by partial N manipulation, or by nearly any other method that is conceivable.
Since channelization of the feedback path is dependent only upon the time required to divide the frequency in the feedback path by a different number, if a channelization voltage is simultaneously applied to the VCO, channelization is extremely rapid.
AC modulation of the forward path, at frequencies above the loop frequency, may be achieved by applying an analog voltage, or modulating voltage, to the VCO via a modulation resistor, as taught in the aforesaid Lautzenhiser patents, or by any other suitable means.
DC modulation of the feedback path may be achieved by digital manipulation of pulses in the feedback path, as taught by Lautzenhiser in the aforesaid patents, or by any other suitable means.
In phase-locked oscillators, an error signal is produced by a difference in a feedback frequency to a reference frequency. This error signal may be integrated by analog or digital circuitry.
In phase-locked oscillators that use an analog integrator, the error signal is time-integrated. This time-integrated error signal, which is a voltage, is applied to the VCO during the integration process. The error signal disappears and integration stops when phase lock is achieved.
In phase-locked oscillators that use a digital integrator, the error signal is integrated by summing clock-timed UP and DOWN error signals. D/A conversion changes the digitally-integrated error signals into voltage which is applied to the VCO during the integration process. Error signals disappear and integration stops when phase lock is achieved.
The frequency-hopping oscillators of the present invention include adaptive circuitry with learning and recalling functions, thereby providing frequency-hopping oscillators in which an output frequency of a VCO can be channelized without waiting for phase locking.
Channelizing information, and/or frequency-correction information, is developed and stored that, when recalled will drive the output frequency to the desired channel almost instantly, and with very little deviation from frequencies that would phase lock for the respective channels.
The channelizing information compensates for errors in proportionality and linearity of such components as a D/A converter, an analog combiner/offsetter, resistor values, and/or a VCO. Subsequent return to the same channelized frequency results in automatic correction for temperature drift of various components that may have occurred since the channel was last accessed.
That is, adaptive circuitry stores channelizing information that can be recalled and converted into a plurality of channelization voltages, one for each channel. Thereafter, the output frequency of the VCO can be driven to channelized frequencies that approach phase lock without waiting for the phase-locked oscillator to phase lock.
The various embodiments include digital integrators and special circuitry that mimics analog circuitry. That is, they each include circuity that provides digital lead compensation, thereby providing loop stability for the digital integrators, even as analog integrators use a lead resistor in series with an integrating capacitor to achieve lead compensation and loop stability.
In first and second embodiments, lead compensation is achieved by analog summation of a channelizing voltage and a lead compensating voltage. In a third embodiment, lead compensation is achieved by digital summation of digitized channeling information and a digital lead-compensation signal.
If a battery back-up is provided in any of the embodiments, at initialization, as each channel is accessed and the frequency-hopping oscillator phase locks to each channelized frequency, the frequency-hopping oscillator learns its channelizing voltage, and the channelizing information that represents each channelizing voltage, is stored in digital form.
If battery retention of volatile memory is not included, upon start-up, as each channel is accessed, the frequency-hopping oscillator phase locks to the respective frequencies. And the RAM stores the channelizing information.
When the channelizing information is recalled from memory and converted to a channelizing voltage, the output frequency of the VCO will be driven to a frequency that will phase lock except for temperature drift of components since last accessing the same channel.
In addition to lead-compensated digital integrators, the present invention includes improved D/A converters. Whereas the primary design objective of prior-art D/A converters has been to produce output voltages that increase linearly in response to increased digital inputs, the improved D/A of the present invention produces analog outputs that are intentionally nonlinear.
That is, whereas prior art D/A converters provide analog outputs in which each higher bit produces a voltage that is twice as high as the next lower bit, the D/A converter of the present invention can be characterized as having an analog output of a higher bit that is less than twice the analog output of the next lower bit.
The improved D/A converter of the present invention also can be characterized as having an analog output of the highest bit that is less than the sum of the outputs of all lower bits.
Further, the improved D/A of the present invention can be characterized as having dual addresses. A D/A converter has dual addresses if the same analog output can be produced in response to two different digital inputs.
Still further, the improved D/A converter of the present invention can be characterized as being without xe2x80x9choles.xe2x80x9d A D/A converter is said to have holes if one digital input produces an analog output that is too low to satisfy a need, such as phase locking, and the next higher digital input produces an analog output that is too high to satisfy a need, such as phase locking. For instance, if an increase in a digital input of 1 produced a voltage step significantly higher than an average, or nominal, voltage step, the hole would reduce the effective resolution of the D/A converter by one bit.
Holes are caused by accumulative errors in resistances in D/A converters. While twelve bit D/A converters are practical and relatively economical, it is difficult and expensive to prevent holes in larger D/A converters because of the large number of resistor tolerances and random accumulation of the resistor tolerances.
Therefore, the present invention provides a nonlinear D/A converter that excels over prior-art D/A converters in both performance and cost when used in adaptive systems such as taught herein.
More particularly, the nonlinear D/A converter of the present invention prevents holes in output voltages, allows lower cost resistors to be used, and allows a larger number of bits to be processed, even when low cost resistors are used.
In a second aspect of the present invention, a method for adaptively producing channelizing information for a plurality of channelized output frequencies comprises: selecting phase-locking parameters for one of the channelized frequencies; producing UP/DOWN signals indicative of phase-locking conditions; digitally integrating the UP/DOWN signals at a clock frequency; and the digital integrating step comprises recalling and digitally storing at the clock frequency.
In a third aspect of the present invention, a method for adaptively producing channelizing information for a plurality of channelized output frequencies comprises: selecting phase-locking parameters for one of the channelized frequencies; producing UP/DOWN signals indicative of phase locking conditions; accumulatively-summing correction signals as a function of the UP/DOWN signals; and the accumulatively summing step comprises repeatedly storing and recalling at a clock frequency.
In a fourth aspect of the present invention, in apparatus for adaptively producing channelizing information for a plurality of channelized output frequencies comprises a phase-locked oscillator having a phase detector, having a forward path that is operatively connected to the phase detector, and having both an integrator and a voltage-controlled oscillator in the forward path, the improvement in which the integrator comprises: a digital storage device; a parallel adder being operatively connected to the digital storage device; and means, comprising the digital storage device and the parallel adder, for summing successive ones of plus one, minus one, or zero correction signals at a clock frequency.
In a fifth aspect of the present invention, in apparatus for adaptively producing channelizing information for a plurality of channelized output frequencies comprises a phase-locked oscillator having an integrator in a forward path, the improvement in which the integrator comprises: means for algebraically-summing successive ones of plus one, minus one, or zero correction signals at a clock frequency; and the means for algebraically summing comprises means for storing and recalling the algebraically-summed correction signals at the clock frequency.
In a sixth aspect of the present invention, in apparatus for adaptively producing channelizing information for a plurality of channelized output frequencies comprises a phase-locked oscillator having a phase comparator that produces UP/DOWN signals indicative of phase-locking conditions, and having a forward path with a voltage-controlled oscillator that produces an output frequency, the improvement which comprises: means, being interposed intermediate of the phase detector and the voltage-controlled oscillator, for recalling and storing digital information at a clock frequency; and means for adding successive ones of a plus one, a minus one, or a zero to the recalled information in accordance with the UP/DOWN signals intermediate of the recalling and storing.
In a seventh aspect of the present invention, in apparatus for adaptively producing channelizing information for a plurality of channelized output frequencies comprises a phase-locked oscillator having a phase comparator, and having a forward path with a voltage-controlled oscillator that produces an output frequency, the improvement which comprises: a digital storage device being operatively interposed intermediate of the phase comparator and the forward path; and a parallel adder being operatively interposed intermediate of the comparator and the forward path, and being operatively connected to the digital storage device; and a clock, being operatively connected to the digital storage device.
In an eighth aspect of the present invention, a method for adaptively producing channelizing information for a plurality of channelized frequencies comprises: recalling previously-stored digital information for one of the channelized frequencies; adaptively correcting the recalled digital information; storing the corrected digital information; and repeating the recalling, adaptively correcting, and storing steps at a clock frequency.
In a ninth aspect of the present invention, a method for adaptively producing channelizing information for a plurality of channelized output frequencies, which method comprises: recalling previously-stored channelizing information for the one channelized frequency; driving an output frequency toward phase lock for the one channelized frequency; producing UP/DOWN signals indicative of phase-locking conditions; digitally integrating the UP/DOWN signals; and the digital integrating step comprises repeatedly recalling and storing prior to recalling channelizing information for an other of the channelized frequencies.
In a tenth aspect of the present invention, a method for adaptively producing channelizing information for a plurality of channelized output frequencies comprises: selecting phase-locking parameters for one of the channelized frequencies; recalling previously-stored channelizing information for the one channelized frequency; driving an output frequency toward phase lock for the one channelized frequency; accumulatively-summing successive ones of correction signals as a function of phase locking conditions; and the accumulatively summing step comprises repeatedly recalling, algebraically adding, and storing prior to recalling channelizing information for an other one of the channelized frequencies.
In an eleventh aspect of the present invention, in apparatus for adaptively producing channelizing information for a plurality of channelized frequencies comprises a phase-locked oscillator, the improvement which comprises: means for recalling channelizing information for one of the channelized frequencies; means for adaptively correcting the recalled channelizing information for the one channelized frequency; means for storing the adaptively-corrected channelizing information; and means for repeatedly repeating the recalling, adaptively correcting, and storing prior to recalling channelizing information for an other of the channelized frequencies.